In the processing and packaging of semiconductor devices, wire and ribbon bonding techniques are often used to provide electrical interconnection between locations within a package (e.g., between a die pad of a semiconductor die and a lead of a leadframe). For example, wire bonding machines (or ribbon bonding machines) are used to form wire loops (or ribbon interconnections) between respective locations to be electrically interconnected. Exemplary methods of forming the interconnections include ball bonding, wedge bonding, and ribbon bonding. An exemplary wedge or ribbon bonding sequence includes: (1) forming a first wedge/ribbon bond on a die pad of a semiconductor die; (2) extending a length of wire/ribbon in a desired shape between the die pad and a lead of a leadframe; (3) forming a second wedge/ribbon bond on the lead of the leadframe; and (4) severing the wire/ribbon to complete the wire/ribbon loop. In forming the bonds between (a) the respective portion of the wire/ribbon material and (b) the respective bond site (e.g., a die pad, a lead, etc.) varying types of bonding energy may be used including, for example, ultrasonic energy, thermosonic energy, thermocompressive energy, amongst others.
A continuous trend in the semiconductor industry is that global markets demand smaller devices at lower costs. One exemplary cost reduction strategy involves using less material in the devices, for example, using less copper material in the leadframe support structure which supports the semiconductor dice. This strategy tends to lead to the creation of highly populated leadframes which support the semiconductor dice (and are used to transport the semiconductor dice) through the manufacturing process. Highly populated leadframes tend to contain many rows and columns of semiconductor dice and other components, where the leadframe portions are connected to the leadframe matrix by connecting portions such as small and thin tie bars. The density and small sizes of the leadframe components makes properly constraining the portions of the semiconductor device (including leadframe portions, die portions, etc.) during the ultrasonic wire or ribbon bonding process very difficult. Clamps (e.g., finger clamps) are typically used to secure the leadframe to a support structure (positioned beneath the leadframe) during a bonding operation. Unfortunately, poor clamping (which may result from the density and arrangement of the components) tends to lead to an unreliable process, and therefore bonded components of a poor quality. For example, because the bonding process (e.g., ultrasonic bonding process) is highly dynamic, particularly for large wire and ribbon bonding, the device being bonded (including the leadframe) may be driven at high velocities similar in amplitude to the tip velocity of the bonding tool used to form the wire/ribbon bonds. In such a case, the relative displacement between the bonding tool and the semiconductor device may be decreased.
FIG. 1A is an overhead illustration of leadframe strip 100 supporting a plurality of semiconductor dice 102. FIG. 1B is a detailed view of the circled portion “1B” of FIG. 1A and illustrates exemplary semiconductor die 102 on heat sink 101 of leadframe 100. Leadframe 100 also includes: source lead 104; leads 104a, 104b, 104c; gate lead 104d; and tie bars 108. Openings 106 are defined between various portions of leadframe 100. It is desired to bond wires or ribbons between conductive locations on die 102 (e.g., die pads, not shown) and corresponding adjacent leads 104.
FIGS. 2A-2D illustrate a conventional approach for securing another leadframe 200, supporting a plurality of semiconductor dice 202, during a bonding operation. FIG. 2A illustrates device clamp 220 positioned above leadframe 200, where device clamp 220 includes flexible clamp fingers 212 that press portions of leadframe 200 within opening 220a of device clamp 220 against lower supporting structure 214 (e.g., anvil 214) during the bonding operation. FIG. 2B is a detailed view of FIG. 2A at circled portion “2B” showing clamp fingers 212 pressing against portions of leadframe 200. Semiconductor die 202 is secured to heat sink 201 of leadframe 200. Leadframe 200 also includes: source lead 204; leads 204a, 204b, 204c; gate lead 204d; and tie bars 208. Openings 206 are defined between various portions of leadframe 200. FIG. 2C is a cross-sectional view of FIG. 2B taken at line “2C-2C”, and FIG. 2D is a detailed view of FIG. 2C at circled portion “2D” of FIG. 2C showing detail of clamp finger 212 pressing against lead 204 proximate die 202 (with the dotted portions being portions of leadframe 200 such as leads 204/tie bars 208). The constraint of leadframe 200 by device clamp 220 in this design is dependent upon the frictional coupling of leadframe 200 to anvil 214 provided by clamping caused by the normal force induced by the bending of clamp fingers 212. In many applications this frictional coupling is not sufficient to properly constrain leadframe 200, and therefore poor bonding tends to result.
Thus, it would be desirable to provide improved clamping systems for wire and ribbon bonding applications.